I never noticed the clock stopping, buit it was probably just cause I wasn't observant enough.

I wonder if this was related at all to my puzzling pfSense stability problems under ESXi 5.0.0 where the DHCP function would just stop working at random intervals. Clients already assigned IP's would continue to work just fine nd data would be routed to them, but new clients would not get IP's and not function at all.

It was a puzzling issue I never quite figured out. In the process of reinstalling with 5.1 now, time will tell if the issue disappears.